1. Field of the Invention
The present invention relates in general to disc cassettes for use in a disc player, and more particularly to the disc cassettes of a type having a sliding shutter by which a part of a disc rotatably disposed in a case (or shell) is selectively exposed and concealed.
2. Description of the Prior Art
In order to clarify the task of the present invention, one conventional disc cassette 101 of the above-mentioned type will be described with reference to FIGS. 11 and 12 of the drawings.
FIG. 11 shows a perspective view of the disc cassette 101, and FIG. 12 shows an enlarged sectional view of a shutter structure of the disc cassette 101, which is taken from the direction of the arrow XII of FIG. 11.
The disc cassette 101 is of a type usually called "3.5 inch microfloppy disc". As is seen from FIG. 11, the disc cassette 101 comprises a disc 102 as a recording medium, a rectangular case (or shell) 105 having the disc 102 rotatably disposed therein, and a shutter structure provided on the case 105 to selectively expose and conceal a part of the disc 102 in the case 105.
As is seen from FIGS. 11 and 12, the shutter structure comprises a rectangular recess 103 formed in each of upper and lower surfaces of the case 105 (see FIG. 12), a smaller rectangular opening 104 formed in the case 105 within the area of each recess 103 to expose a part of the disc 102 to the outside, and a rectangular shutter 106 slidably engaged with the recess 103 to selectively open and close the opening 104.
As is seen from FIGS. 11 and 12, each rectangular recess 103 of the case 105 is defined by two side walls 103a and 103a", a back wall 103a' and a bottom wall 103b.
As is seen from FIG. 11, the shutter 106 is formed with a rectangular opening 109 which is somewhat larger than the opening 104 of the case 105. The shutter 106 is biased toward a closed position by a coiled spring 108 which has one end hooked to the shutter 106 at 107 and the other end hooked to the case 105. That is, in the closed position of the shutter 106, a major solid part of the shutter 106 covers the opening 104, as is shown in the drawing.
When the shutter 106 is slid from the closed position in the direction of the arrow "O" against the biasing force of the coiled spring 108 and takes its open position, the opening 109 of the shutter 106 becomes registered with the opening 104 of the case 105 thereby to expose a part of the disc 102 to the outside.
As is seen from FIG. 12, the back wall 103a' of the recess 103 is formed perpendicular to the bottom wall 103b and the depth "D" of the recess 103 is greater than the thickness "T" of a plate of the shutter 106.
However, due to its inherent construction, the above-mentioned conventional disc cassette 101 has the following drawbacks.
As is seen from FIG. 13, when a plurality of the disc cassettes 101 are put into a cassette holder 202 of a disc player 201 for playing the discs 102 in succession, the disc cassettes 101 are piled up in the cassette holder 202. In fact, such successional playing is widely used when it is needed to record or dub the same information on many discs (viz., dubbing).
However, when the disc cassettes 101 of the above-mentioned conventional type are subjected to such successional playing, smooth loading of each cassette 101 into a drive device 204 (see FIG. 14) is not expected. That is, as is seen from FIG. 14, for the cassette loading, a pusher 203 pushes the lowermost disc cassette 101a of the stack of cassettes 101 toward the drive device 204. However, in this case, it tends to occur that the second cassette 101b from the bottom obstructs the loading movement of the lowermost disc cassette 101a for the following reason.
As is seen from FIG. 15, when the cassettes 101 are stacked in the cassette holder 202, the shutter 106 of the second cassette 101b would be partially put into the recess 103 of the lowermost disc cassette 101a. This is because the depth "D" of the recess 103 is greater than the thickness "T" of the plate of the shutter 106. When, under this condition, the lowermost disc cassette 101a is forced to move leftward in FIG. 15 by the pusher 203, the back wall 103a' of the recess 103 of the lowermost disc cassette 101a is brought into abutment with the leading end of the shutter 106 of the second cassette 101b, which blocks the loading movement of the lowermost disc cassette 101a into the drive device 204.
The total weight of the cassette stack 101 causes a non-negligible deformation of the lowermost disc cassette 101a, which promotes the undesired penetration of the shutter 106 of the second cassette 101b into the recess 103 of the lowermost disc cassette 101a. Furthermore, the perpendicular orientation of the back wall 103a' relative to the bottom wall 103b promotes the undesired blocking engagement of the shutter 106 of the second cassette 101b with the back wall 103a'.
Furthermore, as is seen from FIG. 12, such perpendicular orientation of the back wall 103a' relative to the bottom wall 103b causes collection of dust 111 at the corner of the recess 103 defined therebetween.